Comments and Corrections about the Savonius Super Rotor

Amendments to a previous article, this piece offers updated information about the Savonius Wind Generator System.

| May/June 1974

  • 026-078-03.jpg
    The Savonius super rotor is a vertical wind generator design originally introduced to the U.S. in 1924.
  • 027-038-01-S-Rotor
    A large-scale Savonius rotor can be constructed more cheaply than the more familiar propeller-driven wind generators.

  • 026-078-03.jpg
  • 027-038-01-S-Rotor

Here are a few comments and corrections pertaining to my article The Savonius Super Rotor in the March/April 1974 issue of MOTHER EARTH NEWS.

[1] In case you were wondering, that's not me with the shirt off in that Image Gallery picture . . . that's David House (resident and founder of Earthmind and author of the book Methane Systems ), as photographed late in November. Yep, it were cold, but then we are real hardy folk, too.

[2] My comparison of the Stuart mill and the Savonius rotor omitted any mention of feathering: twisting of a conventional windplant's propeller blades to lower the device's rotational speed in high winds. (See Marcellus Jacobs: Wind-Power Generating Inventor for a discussion of the subject — MOTHER.) 

Feathering is a necessary precaution in wind-charger design for a number of reasons. First — whenever a fixed gear ratio is used, some such governing arrangement is needed to prevent the alternator/generator from exceeding its maximum rated output (current). In a propeller-driven unit, however, the prop itself is a factor in determining at what windspeed feathering must occur. The problems involved may be described in terms of balance, structural design and blade tip stresses.

[a] Balance — as I mentioned in my article — is always more important (or critical) at higher rotational speeds than at lower rpm's. If a propeller is allowed to exceed its "operating range," therefore, dangerous vibrations can be set up.

[b] The structural design of a propeller, and the materials of which it's made, also determine the device's upper rotational speed beyond which centrifugal force will pull it apart.

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